The present invention relates to fine ceramic particles formed in-situ in metal and in alloys by the liquid-state process, and to products containing the fine ceramic particles formed in-situ in metal and in alloys by the liquid-state process. In one aspect, the present invention relates to a process for producing a material containing uniformly dispersed, finely sized ceramic phase particles, e.g., such as titanium carbide particles, formed in-situ in metals and in alloys by the liquid-state process.
The aluminum and aerospace industries have long sought a method to ran control recrystallization of aluminum alloys during deformation operations to permit the design of aluminum airframes with improved structural properties.
The metals industry today conventionally uses dispersoids, i.e., fine particles dispersed in the metal alloy, to control recrystallization and to increase dispersion strengthening at elevated temperatures. Such dispersoids of fine particles dispersed in the metal alloy usually are formed by solid state precipitation.
Recent developments in this area suggest that to improve formability and high temperature strength of aluminum alloys, it is necessary to increase the number densities and to reduce the size of the fine particle size dispersoids.
Certain emerging technologies are capable of producing fine particulates of different types with somewhat improved interfacial characteristics. Among the several ways of producing these materials, the technologies where the particles are introduced or formed in the molten aluminum prior to its solidification are attractive, primarily because of the potential for commercially economic processes on a large scale.
A variety of processing routes classified generally as in-situ ceramic phase formation processes in metal have been developed recently. According to the state of the reactants in the process, such a ceramic phase formation process in metal generally is classified into one of several categories:
(1) liquid metalxe2x80x94gas reaction,
(2) liquid metalxe2x80x94liquid metal reaction, or
(3) liquidxe2x80x94solid reaction.
In the case of carbon particles or carbon blocks in the context of liquid metalxe2x80x94liquid metal reactions or liquidxe2x80x94solid reactions, it is known that such carbon particles or carbon blocks are difficult to introduce directly into a melt in metal because of non-wetting of the carbon by the molten metal or alloy.
Recent developments in liquid metalxe2x80x94gas reaction processes have produced fine TiC particulates in a molten aluminum alloy. In this approach, a carbonaceous gas is introduced into an aluminum melt containing titanium to form TiC particulates, and the carbide volume fraction is determined by the initial titanium content. When the melt containing the carbides is cast and subsequently extruded for microstructure and property evaluation, the as-cast microstructure of the in-situ processed composites reveals a relatively uniform distribution of TiC particles with an average size of a few microns. No preferential particle segregation is observed in the dendritic cell boundaries generally.
U.S. Pat. No. 4,808,372, issued to Koczak et al., discloses an in-situ process for producing a composite containing refractory material. A molten composition, comprising a matrix liquid, and at least one refractory carbide-forming component are provided, and a gas is introduced into the molten composition. Methane is bubbled through a molten composition of powdered aluminum and powdered titanium to produce a carbide having an average particle size in the fine mode of about 3 to 7 microns and in the coarse mode of about 35 microns.
Although conventional ceramic phase formation processes in metal offer some possibilities for the production of a wide range of reinforcement particle types and improved compatibility between the reinforcement and the matrix, the in-situ formed ceramic particles in metal are too large, e.g., on the order of several microns, and tend to form clusters. In-situ formed ceramic particles having these sizes, i.e., of several microns, are candidates for use as reinforcement in a composite, but are not suitable for use as dispersoids for recrystallation control, for dispersion strengthening, or for use as a component for structure refinement.
Accordingly, a novel ceramic dispersoid in metal product and process for making such a novel ceramic dispersoid in metal product are needed for providing uniformly dispersed, finely sized ceramic phase particles dispersed in-situ in a metal matrix.
U.S. Pat. Nos. 4,842,821 and 4,748,001, issued to Banerji et al., disclose a method for producing a metal melt containing dispersed particles of titanium carbide. Carbon particles are reacted with titanium in the metal to obtain titanium carbide. The patent discloses that salts preferably are entirely absent from the melt (U.S. Pat. No. 4,842,821, col. 3, lines 26-28, and U.S. Pat. No. 4,748,001, col. 3, lines 40-42).
U.S. Pat. No. 5,405,427, issued to Eckert, discloses a flux composition for purifying molten aluminum to remove or capture inclusions in the melt and carry such inclusions to the surface (col. 4, line 13 et seq.). The flux composition contains sodium chloride, potassium chloride, and a minor amount of magnesium chloride and carbon particles.
U.S. Pat. No. 5,401,338, issued to Lin, discloses a process for making metal matrix composites wherein fine particles (0.05 microns) of alumina, silicon nitride, silicon carbide, titanium carbide, zirconium oxide, boron carbide, or tantalum carbide are added into a metal alloy matrix (col. 2, lines 64-68).
U.S. Pat. No. 5,041,263, issued to Sigworth, discloses a process for providing a grain refiner for an aluminum master alloy that contains carbon or other third, elements and acts as an effective refiner in solution in the matrix, rather than being present as massive hard particles.
Uniformly high number densities of finely sized dispersoids increase the recrystallization temperature, inhibit grain growth in hot working, and improve elevated temperature strength. Further, fine particles of dispersoids are effective nuclei for grain refining.
It is against this need in the background technology that the present invention was made.
Accordingly, it is an object of this invention to provide aluminum alloys having high number densities of fine ceramic particles to act as dispersoids.
Accordingly, it is an object of the present invention to provide a method for increasing the number densities of dispersoids in the liquid state and which then remain stable and dispersed in the solid state in metal alloys.
It is an object of the present invention to produce finely sized ceramic phase particles.
It is a further object of the present invention to produce uniformity in the dispersion of finely sized ceramic phase particles in metal and in alloys.
It is yet another object of the present invention to produce uniformly distributed, finely sized ceramic phase particles dispersed in-situ in a metal matrix.
It is another object of the present invention to produce uniformly distributed, finely sized ceramic phase particles dispersed in-situ in a metal alloy in a process providing reaction times shorter than conventional approaches.
It is another object of the present invention to produce uniformly distributed, finely sized ceramic phase particles dispersed in-situ in a metal alloy for rectystallization control, dispersion strengthening, or grain refining.
These and other objects of the present invention will become apparent from the detailed description which follows.
The present invention provides a novel method for producing a ceramic phase particle dispersoid in metal and a novel product composed thereof. The method includes (a) providing a molten composition consisting essentially of molten aluminum alloy and molten metal selected form the group consisting of Zr, V and combinations thereof; (b) providing a chloride salt containing fine carbon particles; and (c) reacting the chloride salt containing fine carbon particles in the molten aluminum metal liquid with the molten metal liquid to form a uniform distribution of finely sized carbide particles formed and dispersed in-situ in an aluminum alloy matrix.
The step of reacting includes vigorously stirring the mixture containing salt, metal alloy, and carbon to form a reaction mixture at a temperature above the liquidus of alloy to form a uniform distribution of particles sized less than about 2.5 microns uniformly dispersed in-situ in the metal matrix.
Another embodiment of the invention is a ceramic dispersoid in metal product comprising: (a) a matrix metal; and (b) a uniform distribution of formed and dispersed in-situ in the metal matrix. The finely sized ceramic particles are formed by the process of: (i) providing a molten composition comprising a matrix liquid of aluminum or aluminum alloy metal and at least one carbide-forming element selected from the group consisting of Ti, Sc, Hf, Nb, Zr, Mo, and V; (ii) providing a chloride salt containing carbon particles, wherein the salt comprises NaCl and KCl in a weight/weight ratio within the range of about 0.8xe2x80x941.2 and of MgCl2 and CaCl2 in amounts comprising up to about 5-10% by weight of the salt mixture; and (iii) reacting the chloride salt containing carbon particles in the molten aluminum alloy by vigorously stirring the aluminum alloy and the chloride salt containing carbon particles to form a mixture of the molten metal liquid in contact with a portion of the carbon particles at an elevated temperature above the liquidus of the aluminum alloy to form a unagglomerated distribution of finely sized ceramic phase particles having an average particle diameter of less than about 0.3 microns formed and dispersed in-situ in an aluminum metal matrix;